package main

import "fmt"

// Stack is a stack of integers with no defined max depth
type Stack struct {
	values []int
}

// Pop returns the top of the stack
func (s *Stack) Pop() (int, error) {
	if len(s.values) == 0 {
		return 0, fmt.Errorf("stack empty")
	}
	i := s.values[0]
	s.values = s.values[1:]
	return i, nil
}

// Push adds a value to the top of the stack
func (s *Stack) Push(i int) {
	s.values = append([]int{i}, s.values...)
}